The present invention relates to an illuminating device for illuminating background surfaces, especially for surface displays comprising a circuit board, made of a light-transmissive material and covered with a non-light-transmissive material, and light-emitting diode chips arranged on the circuit board and controllable by leads, and further having a housing supporting the background surface to be illuminated, the housing having reflecting surfaces.
An illuminating device of the aforementioned kind is known from PCT application WO 90/13885. In one embodiment of the illuminating device disclosed therein a circuit board with light-emitting diode chips is supported on a plastic frame provided with reflecting surfaces. Opposite to the circuit board the background surface to be illuminated is arranged and is in the form of a diffuser film. The essentially light-transmissive circuit board is coated with a non-light-transmissive metal or other material with the exception of the leads and the light-emitting diode chips so that the light generated by the light-emitting diode chips is emitted only in the direction toward the background surface to be illuminated. With this known design it is said to be possible to produce illuminating devices of a total constructive height of only 2 mm to 3 mm.
However, the known illuminating device has the disadvantage that a further reduction of the constructive height is not possible because the required closer placement of the background surface to be illuminated and the arranged circuit board with the light-emitting diode chips prevents the diffusion and distribution of the emitted light of the light-emitting diode chips. The illumination of the background surface occurs essentially with a point focus with a visible transmission of the chip arrangement onto the background surface, which thus exhibits great light differences.
It is therefore an object of the present invention to provide an illuminating device of the aforementioned kind that is improved with respect to minimizing its constructive height and a uniform illumination of the background surface.